Nowadays, due to the increasing depletion of fossil fuels, exploring the clean renewable energy resources has become an urgent issue. Biomass, including cellulose, hemicellulose, and lignin, is one of the most widely renewable resources in the world. Cellulose and hemicellulose have been widely used, while lignin which accounts for 25% of the lignocellulosic biomass, is still not commonly used, which causes waste of resources and pollution of the environment. There has been many researches performed on the conversion of lignin, which includes pyrolysis, base hydrolysis, supercritical water hydrolysis etc. However, these methods mentioned above need harsh reaction conditions and always give low product yields. Therefore, the development of a fast, effective and environmentally friendly method of lignin depolymerization has attracted the attention of researchers. Lignin is a three dimensional amorphous polymer in which methoxylated phenylpropanes are connected with ether and carbon-carbon bonds. Lignin, as a primary component of plant biomass, contains many oxygen functional groups (hydroxyl, carboxyl, carbonyl groups, ether and ester bonds). Therefore, phenolic chemicals can be obtained from lignin by a chemical degradation processes. There are two major challenges for the application of lignin as a source of chemicals and materials. Firstly, the polyphenolic structure is chemically very stable, and therefore, difficult to transform or structurally modify. Moreover, it contains a large amount of functional groups which facilitate the condensation reactions during the depolymerization.